1. Field of the Invention
This invention relates to a knocking control apparatus of an internal combustion engine for controlling ignition timing in accordance with the presence of knocking.
2. Description of the Prior Art
A knocking controlling system having a microprocessor (MPU) for detecting knocking in addition to a microprocessor for controlling of knocking is known. In such prior art knocking system, the detection result of knocking is sent from the knocking detection microprocessor to the knock control microprocessor. Such technique is disclosed in Japanese patent application provisional publication No. 59-46519 (U.S. Pat. No. 4,498,331), No. 1-315647 (U.S. Pat. No. 4,993,387) and Japanese patent publication No. 63-42112.
However, in such systems, when a communication port is failed and the knocking detection microprocessor detects the presence of knocking, the knocking control microprocessor may judge that there is no knocking.
The reason is as follows:
If knocking detection result is represented by combination of levels of output ports Q2 and Q3 in the communication signal lines between the knock detection microprocessor and the knocking control microprocessor, the knocking detection result is, for example, as follows:
TABLE 1 ______________________________________ low medium large knocking no degree degree degree detection result knocking of knocking of knocking of knocking ______________________________________ port Q2 0 1 0 1 port Q3 0 0 1 1 ______________________________________
Therefore, there is a problem that the internal combustion engine is damage because the phase lag control is not carried out though knocking occurs when the ports Q2 and Q3 for outputting the knocking detection result or the signal lines for commemoration between two microprocessors are failed, so that the ports Q2 and Q3 are fixed to zero level.